The present invention relates to a system for the conversion of iron-ore into iron-ore pellets or directly into highly metalized sponge iron. More specifically, the present invention relates to an improved tail shaft assembly for use in a traveling grate of the above system.
Generally, known direct reduction systems consist of a traveling grate, a ported or non-ported rotary kiln, and a rotary cooler connected in series. Pelletized iron-ore concentrate is fed to the oxidizing traveling grate for drying and preheating in order to provide strength to the iron-ore pellets. The hot, preheated pellets are then fed directly into the rotary kiln. Solid fuel, such as coal or other processing agents, can be added to the traveling grate and discharged along with the iron-ore pellets into the rotary kiln. In the case of a ported kiln, natural gas, oil or other fluid fuels can be introduced to the ports. Pellets discharging from the lower end of the kiln are then cooled in the rotary cooler and output for further downstream processing.
In the above-described and known system, the traveling grate used in drying and preheating the pellets generally includes a series of spaced lateral slats mounted between a plurality of individual drive chains. Each of the drive chains is entrained between a downstream drive shaft and an upstream tail shaft. The drive shaft is powered to cause the traveling grate to rotate between the drive shaft and the tail shaft.
Preferably, the tail shaft includes a plurality of spaced rollers that each support one of the drive chains as the drive chain is pulled around the tail shaft. Each of these individual rollers is generally smooth and is secured to the tail shaft to rotate with the tail shaft and guide the drive chains and attached slats. In addition to the plurality of rollers, the tail shaft typically includes a guide sprocket that is secured to the tail shaft. The guide sprocket includes a plurality of individual teeth spaced along its outer circumference. The spacing or pitch between the teeth on the guide sprocket is selected such that each tooth receives a link of the drive chain as the drive chain moves around the rotating tail shaft. Since the tail shaft is typically not driven, the guide sprocket does not exert rotational force on the drive chain but simply functions to maintain proper lateral alignment of the traveling grate along the tail shaft.
As the traveling grate drive chains become worn, the chain pitch length between adjacent links of the drive chain increases. Since the spacing between the teeth along the outer circumference of the drive sprocket remains constant, the chain wear causes the individual links of the drive chain to enter the guide sprocket late. As the wear and misalignment of the chain links along the guide sprocket continues to worsen, the chain links eventually contact the leading edge of the tooth surface. Further use of the guide sprocket and drive chain eventually causes both the drive chain and the guide sprocket to become worn and eventually may cause the drive chain to disengage from the guide sprocket.
Therefore, it is an object of the present invention to provide an improved guide sprocket assembly that can be attached to the tail shaft and can compensate for wear in the drive chain. It is a further object of the invention to provide a guide sprocket assembly having a lock plate assembly secured to the tail shaft and a guide sprocket that is freely rotatable relative to the lock plate assembly. It is a further object of the invention to provide a sprocket retainer between the guide sprocket and the lock plate assembly such that the sprocket retainer retains the guide sprocket in an annular sprocket groove formed in the lock plate assembly and allows the guide sprocket to freely rotate relative to the lock plate assembly.